Gemology or gemmology is the geoscience of gemstone materials and a branch of mineralogy and gemologists are related academic people to identify and evaluate gems.
Uncut and unprocessed gems are usually ordinary rocks. After cutting and polishing, their brilliance and luster come that give them their true value.
There are semiprecious gems and precious gems. Diamonds, rubies, sapphires, and emeralds fall into precious category. These are really rare, thus too valuable. Amethyst was once a precious gem, until large reserves were found in Brazil.
Since precious gems are not very abundant on Earth, they are very expensive (especially diamond). Let's skip those and look at other gemstones for now.
Amber is fossilized tree resin known since Neolithic times as a gemstone. Amber has been used as a healing agent in folk medicine as well as jewelry. Because it originates as a soft, sticky tree resin, amber sometimes contains animal and plant materials.
According to myth, when Phaëton son of Helios (the Sun) was killed, his mourning sisters became poplar trees, and their tears became amber (in Greek elektron meaning beaming Sun). Because of amber's ability to hold static electricity, amber and electricity share a connected history.
Amethyst is a violet variety of quartz. Its name comes from Greek word amethystos, meaning not intoxicate. Ancient Greeks wore amethyst and carved drinking vessels from it in the belief that it would prevent intoxication.
Amethyst, a semiprecious stone, is often used in jewelry and is the traditional birthstone for February.
Aquamarine is a pale-blue to light-green variety of beryl mineral. Its name means water of the sea, from the the Latin words aqua and marina.
Dark variant of raw and cut aquamarine
Aquamarine is the birthstone for March.
Moonstone is a pearly and opaque gemstone with a distinguishing glowing effect.
Moonstone is a birthstone for June, along with pearl and alexandrite.
Turquoise is an opaque, blue-to-green mineral. The word turquoise dates to the 17th century and is derived from the French turquois meaning Turkish because the mineral was first brought to Europe through Turkish territory (Turkey or Turkestan).
Turquoise is the traditional birthstone for December. Ancient Egyptians called turquoise mefkat meaning joy and delight.